Silk screen printing is an old, well-established and popular process. In essence, it involves the preparation of a screen of cloth, normally fine fibrous nylon or polyester, having a photosensitive layer. The coated screen is exposed to the image of the artwork to be printed. In areas where the photosensitive emulsion is exposed to light, the emulsion cures and renders the screen impermeable to the printing ink composition. In areas protected by the image of the artwork, the emulsion remains uncured and can be washed away. Now the screen can be used to print the image of the artwork, by permitting ink to pass through onto a workpiece in a pattern corresponding to the image produced.
To print with the silk screen so formed, it is usual to mount a workpiece below but separated slightly from the screen, apply printing ink of suitable formulation and consistency to the top of the screen, and brush the ink across the top of the screen by means of a squeegee applicator.
Many screen printing operations are of the small scale, custom order variety. It is necessary that the screen printing apparatus used in such an operation be capable of handling a very large variety of different printing jobs, and that it be readily adjustable from one job to another. Such an apparatus must not only be versatile and readily adjustable in several different senses, but it should also be simple and economical to construct and operate, since the scale of such operations normally does not permit capital expenditures for large, powerdriven, mechanized printing apparatus.
A custom order screen printing operation may be called upon to conduct printing upon widely varying objects. For example, it may be necessary to print a repeating pattern upon a set of textiles, for example sports team uniforms. Such a set of articles is small in number, but nevertheless may require fairly intricate printing patterns, e.g. team crests and insignia and sometimes involving multiple colours. The same operation may also be called upon to print upon three-dimensional objects of substantial thickness, such as hockey pucks. It is desirable that a small printing operation have a single machine with sufficient versatility to handle all of such operations.